The goal of this project is to learn more about the control of movement in normal humans and in patients with voluntary movement disorders such as Parkinson's disease, cerebellar ataxia, hemiplegia from stroke and dystonia. The tools we use include clinical neurophysiological methods such as electroencephalography, electromyography, and transcranial magnetic stimulation and neuroimaging with positron emission tomography and functional magnetic resonance imaging. Currently active projects in the Section include analysis of the bradykinesia in Parkinson's disease, studies of recovery from hemiplegia, and the physiology of dystonia. One major scientific target of the Branch is to understand and possibly influence cortical reorganization in patients with congenital or acquired lesions of the central nervous system. A multi-modality approach (neuroimaging with PET and functional MRI, EEG, and transcranial magnetic stimulation) is being used to determine patterns of long-term reorganization of functional brain topography in individual stroke patients. Analysis of data from patients with subcortical lesions indicated that the reorganization of the cortical activity and excitability patterns depends on the site of the lesion within the internal capsule. We tested whether the ipsilateral sensorimotor cortex plays some role in stroke recovery by evaluating the strength of cortico-muscular functional coupling. There was no significant coherence between EEG over the ipsilateral sensorimotor cortex and EMG indicating no emergence or enhancement of the ipsilateral direct cortico-muscular connection. To test the validity of macroscopic coherence measurements using EEG, we performed an experiment using an object detection task. Right and left hemispheres must communicate with each other to constitute the neural correlate of a unitary visual stimulus spanning the visual midline. The interhemispheric coherence revealed a significant increase in 8-12 Hz at 117-373 ms following the target stimuli. This transient coherence increase did not occur with meaningless objects or when the detection of the familiar object failed suggesting that a certain level of neural synchrony is a prerequisite for visual awareness. Spatial discrimination was evaluated in patients with hand dystonia. Compared to normal matched controls, dystonia patients have increased threshold for detection of spatial frequency and a larger localization error. This abnormality in spatial discrimination, together with abnormal temporal discrimination, support the hypothesis that a dysfunction of the sensory system may be relevant to the pathogenesis of dystonia. EEG power changes associated with voluntary muscle relaxation were evaluated in normal subjects. It is associated with a pattern of EEG desynchronization of similar magnitude and cortical topography to that associated with voluntary contraction, but with a subsequent greater EEG synchronization. This indicates that relaxation is an active process of the brain. In order to explain why people more likely to fall backward than forward, we studied subjects perturbed by a translational pushing device. We found that limitations to balance can be predicted by position and velocity of the center of mass of the body. Asymmetry of the tendency to fall is due to the asymmetry of the functional foot length. We scanned, using an event-related fMRI design, normal subjects while they were performing internally and externally triggered movements with their right index finger. Within the pre-supplementary motor area the activation was significantly higher for internally triggered movements, while within the supplementary motor area proper there was no significant difference between internally and externally triggered task. This suggests a dominant role of the anterior region in the self-initiation of movements.